[TMC] RF amp meters for a TAC-1

[John Poulton]

Edmund,

I'd love to see photos of your '551 as well, and if you're willing, I'll
post them on the tmchistory website.  Anything you'd like to write up about
getting this rig back into operation would be useful, too!

There's a slight possibility I have a spare meter for the TAC-1.. I'll
check the various locations around the shack over the next couple of days.

73, John K4OZY


On Mon, Apr 28, 2014 at 9:09 PM, John Vendely <jvendely at cfl.rr.com> wrote:

> Hi Ed,
>
> Unfortunately, I have no spare meters, so I can't help you out there.
>  Finding original meters will be tough, but there are some good replacement
> options.  Are your meters missing, or simply defective?  I would also
> recommend checking the external RF thermocouples.  Blown thermocouples are
> very common in these tuners due to gross abuse, but they are sometimes
> repairable.
>
> My TAC-1 had fallen into the hands of barbarians, and although it was in
> physically excellent condition in every other respect, both RF
> thermocouples were blown, and one meter had been  replaced with an AC
> ammeter, a completely ridiculous substitute.  I scrounged up a Triplett
> meter of the same style (commonly available with various movements), and
> made a new dial plate by duplicating the original meter's dial plate on an
> ordinary copy machine using heavy stock paper.  I trimmed the copied dial
> to slightly oversize, glued it in position on the substitute meter face,
> then carefully scraped around the edges to eliminate the excess paper.
> Believe it or not, this extremely crude expedient actually worked out
> beautifully, and you can't distinguish the replacement meter from the
> original.
>
> Fortunately, the external thermocouples can sometimes be repaired with
> some tedious effort under a microscope.  Each end of the thermocouple wire
> is bonded to two terminal "bars" connected to the external screw terminals.
>  The thermocouple wires have some excess length, and if they're burnt out
> at a point near one of the terminal bars, they can be detached,
> repositioned, and silver-soldered to the terminal bars.  You gotta use a
> stereoscopic microscope, and work carefully with tweezers (the type used
> for surface mount component work).
>
> I figured that after this operation, the thermocouples would never work
> worth a damn again, but I was pleasantly surprised to find this wasn't
> true.  The original meter could be easily calibrated against an accurate
> true RMS AC ammeter using a load resistor and variac at 60 cps, and showed
> good accuracy across the scale.  The replacement meter was then calibrated
> against the original.  One last check was done at 7 Mc with the tuner
> adjusted into a large 600 ohm load resistor, and driving it at 1 kW from a
> SBT-1K transmitter.
>
> I'd love to see a pic of your DDR-551.  I have one of those as well,
> probably not too many of them were made.  I'm looking for the IF, audio,
> and AFC units to complete a DDR-5, if you (or anyone else) has any for sale
> or trade...
>
> 73,
>
> John K9WT
>
>
> On 4/28/2014 7:03 PM, edmund weber wrote:
>
>>   Greetings to the Forum,
>>       I am posting this in hopes of finding the RF amp meters that are
>> used in the TAC-1 antenna tuner...it's a long shot, but I know there's a
>> pair
>> out there somewhere! My DDR-551 is almost finished, needing only the AF
>> and IF filter units, and the AC control panel.
>>       I have several  TMC items that are surplus to my needs for sale or
>> trade as well.
>>   Thanks,
>>   Ed, KA6ZMI
>>   Near San Francisco
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